Summary of Significant Accounting Policies (Details 2) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Earnings Per Share
Preferred stock, shares outstanding	12,050		12,050		12,275
Net income loss available to common stockholders
Net income	$ 41,317,000	$ 46,446,000	$ 94,408,000	$ 191,732,000
Net income applicable to preferred stock	7,691,000	8,990,000	17,692,000	37,165,000
Net income applicable to common stock	33,626,000	37,456,000	76,716,000	154,567,000
Determination of shares:
Weighted-average common shares outstanding (in shares)	78,635,000	76,336,000	78,169,000	76,196,000
Assumed conversion of dilutive employee stock-based awards (in shares)	2,929,000	2,059,000	3,020,000	2,243,000
Assumed conversion of restricted stock (in shares)	111,000	168,000	101,000	157,000
Assumed conversion of preferred stock (in shares)	21,767,000	27,278,000	21,817,000	27,278,000
Diluted weighted-average common shares outstanding (in shares)	103,442,000	105,841,000	103,107,000	105,874,000
Anti-dilutive securities, options to purchase shares outstanding	20,625	4,353,529	30,625	3,132,000
Calculation of basic EPS:
Net income applicable to common stock	33,626,000	37,456,000	76,716,000	154,567,000
Weighted-average common shares outstanding (in shares)	78,635,000	76,336,000	78,169,000	76,196,000
Basic earnings per common share	$ 0.43	$ 0.49	$ 0.98	$ 2.03
Calculation of diluted EPS:
Net income	41,317,000	46,446,000	94,408,000	191,732,000
Diluted weighted-average common shares outstanding (in shares)	103,442,000	105,841,000	103,107,000	105,874,000
Diluted earnings per common share	$ 0.40	$ 0.44	$ 0.92	$ 1.81
Common stock price less than $45
Determination of shares:
Common stock price (in dollars per share)	$ 45		$ 45
Increase in diluted weighted-average common shares outstanding			26,777,778
Common stock price between $45 and $67
Determination of shares:
Aggregate liquidation preference of preferred stock	$ 1,205,000,000		$ 1,205,000,000
Common stock price between $45 and $67 | Maximum
Determination of shares:
Common stock price (in dollars per share)	$ 67		$ 67
Increase in diluted weighted-average common shares outstanding			26,777,778
Common stock price between $45 and $67 | Minimum
Determination of shares:
Common stock price (in dollars per share)	$ 45		$ 45
Increase in diluted weighted-average common shares outstanding			17,985,075
Common stock price more than $67
Determination of shares:
Common stock price (in dollars per share)	$ 67		$ 67
Increase in diluted weighted-average common shares outstanding			17,985,075